System and method for influencing the induction gas temperature in the combustion chamber of an internal combustion engine

ABSTRACT

The invention relates to a system and method for use in a homogeneous charge compression ignition (HCCI) combustion engine that is preferably equipped with an exhaust gas recirculation device. This system and method enable an improved adjustment of the temperature level inside the combustion chamber. In addition to adjusting the temperature by using the exhaust gas recirculation device, an influencing of the temperature, which is independent thereof, ensues based on the compression of the induced fresh air by the exhaust gas turbocharger. An increase in temperature is maintained even after the compressed air is expanded on a throttle valve, and this increase in temperature can, in the end, be used for influencing the energy content inside the combustion chamber.

CROSS REFERENCE TO RELATED APPLICATION

This application is the US National Stage of International ApplicationNo. PCT/EP2004/002670, filed Mar. 15, 2004 and claims the benefitthereof. The International Application claims the benefits of GermanPatent applications No. 10319330.8 DE filed Apr. 29, 2003, all of theapplications are incorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The invention relates to a system for influencing the induction gastemperature and thereby the energy level in the combustion chamber of aninternal combustion engine, especially of an HCCI-enabled internalcombustion engine with a compression device for compressing inducedfresh air, which before compression has a temperature T₁, as well asexpansion means which cause the compressed induced fresh air to expand,with the compressed and subsequently expanded fresh air having atemperature T₂>T₁.

The invention further relates to a method for influencing the inductiongas temperature and thereby the energy level in the combustion chamberof an internal combustion engine, especially of a HCCI-enabled internalcombustion engine, in which induced fresh air, which before thecompression has a temperature T₁, is compressed, and the compressed,induced fresh air is expanded, where the compressed and subsequentlyexpanded fresh air has a temperature T₂>T₁.

BACKGROUND OF THE INVENTION

Different operating conditions are known in conjunction with directpetrol injection systems. The common factor is that fuel is injectedunder high pressure directly into a combustion chamber. The mixture isthen formed within the combustion chamber. Conventionally a distinctionis made between the homogeneous and lean operating modes. In homogenousoperation a mixture is present which is distributed homogeneously overthe entire combustion chamber. In stratified or lean injection operationthere is only a mixture with a excess air in factor the area of thespark plug λ≦1. The remaining volume of the combustion chamber is filledwith induced fresh air, an inert gas from the exhaust gas recirculationor a very lean fuel-air mixture, so that overall an excess air factor ofλ≦1 is produced.

In addition to these conventional operating modes, a further operatingmode is increasingly being seen as promising, which is similar to theoperation of the self-ignition diesel engine. This is known as HCCI(Homogeneous Charge Compression Ignition) operation and represents anauto-ignition combustion process, in which the time of ignition andthereby the sequence of combustion is controlled via the reactivequantity of energy in the cylinder. To provide a sufficient energy leveluse is usually made of exhaust gas recirculation via external settingmeans within the framework of exhaust gas recirculation or by a suitablegas exchange valve control within the framework of an internal exhaustgas recirculation.

For setting of the temperature level and thereby the energy level in thecombustion chamber via the exhaust gas recirculation rate however it isnecessary to take into account that this can only take place withinspecific limits. Since the exhaust gas recirculation rate influences notonly the temperature level in the combustion chamber but also themixture ratio of air, fuel and exhaust gas, it is under somecircumstances not possible to select an exhaust gas recirculation ratewhich is optimum both with regard to the temperature in the combustionchamber and with regard to the said air-fuel mixture ratio. Thuscompromises can be necessary when setting the exhaust gas recirculationrate to ensure reliable operation of the internal combustion engine.

In the context of conventionally ignited internal combustion engines ithas already been proposed that a cooled exhaust gas recirculation beused, whereby this cooling of the exhaust gas is aimed especially atreducing the nitric oxide emissions. In this context reference is madefor example to the German periodical MTZ Motortechnische Zeitschrift 60(1999) 7/8, page 470 ff.: “Einhaltung zukünftiger Emissionsvorschriftendurch gekiihlte Abgasrückführung” (complying with future emissionregulations using cooled exhaust gas recirculation) by Karl-HeinrichLosing and Rainer Lutz.

SUMMARY OF THE INVENTION

The object of the invention is to overcome the disadvantages of theprior art and especially to provide a system and a method through whichsetting the temperature in the combustion chamber of the internalcombustion engine can be decoupled at least partly from the setting ofthe optimum mixture ratio of air, fuel and exhaust gas.

This object is achieved with the features of the independent claims.

Advantageous embodiments of the invention are specified in the dependentclaims.

The invention builds on the generic system in that the temperatureincrease of the fresh air from T₁ to T₂ is explicitly used to influencethe temperature level and thereby the energy level in the combustionchamber. In this way very fine variations and settings of the energylevel in the combustion chamber can be achieved by increasing thetemperature or by regulating the air/fuel temperature. In this way thecombustion process in the HCCI mode can be precisely controlled. Thetemperature level in the combustion chamber can in this case beinfluenced via the level of compression and the subsequent expansion.

The inventive system is developed in a particularly useful way in thatan exhaust gas recirculation device to feed in exhaust gas from aprevious combustion cycle to fresh air or to a mixture featuring freshair is provided so as to supply, after the injection of fuel, anair/fuel/exhaust gas mixture with an energy level advantageous forcombustion. As well as influencing the temperature level throughcompression and expansion the exhaust gas recirculation and in this caseespecially the exhaust gas recirculation rate can also be explicitlyused to adjust the energy level in the combustion chamber.

The inventive system can then be used to particularly good effect if thecompression device is an exhaust gas turbocharger. This is a frequentlyused device for increasing the gas density in the induction system, sothat in the combustion chamber an increased volume or air can beprovided which results in an increase in performance of the internalcombustion engine. The compression device is driven by a turbine locatedin the exhaust gas stream.

The system can also be used to good effect when the compression deviceis a compressor. This is also used to compress the gas pressure in theinduction system, with the drive energy being supplied mechanically bythe internal combustion engine. As an alternative the compressor canalso be driven by means of electrical energy.

There is useful provision for the compression to be undertaken on athrottle valve. With direct injection systems the throttle valve is usedfor dosed feeding of fresh air, with the throttle effect causing areduction in pressure. Finally the air compressed in the exhaust gasturbocharger or the compressor and expanded on the throttle valve has,in accordance with the basic laws of thermodynamics, a highertemperature than the originally induced fresh air.

The invention is developed in a particularly advantageous way in that atemperature sensor to record the temperature T₂ in the direction of flowof the fresh gas is disposed downstream from the expansion means so thatthis can be taken into account within the framework of a regulation ofthe induction gas temperature. The temperature of the fresh airdownstream from the throttle valve is thus an important input variablein finally advantageously defining the energy level in the combustionchamber for the HCCI operating mode.

In conjunction with a system equipped with exhaust gas recirculation itproves to be especially useful for at least one heat exchanger operatingas an exhaust gas cooler for lowering the temperature of therecirculated exhaust gas to be provided and for a cooling means settingvalve to be provided so that by influencing the cooling meansthroughflow through the exhaust gas cooler, taking into account measuredvalues or values determined from a technical model, the induction gastemperature can be set or regulated respectively. The recirculatedexhaust gas volume is thus no longer compulsorily coupled to thetemperature increase in the combustion chamber achieved by exhaust gasrecirculation. Instead the energy content in the combustion chamber canbe adjusted within certain limits independently of the exhaust gasrecirculation rate via the adjustable exhaust gas cooling. Thus both themixture ratio and the energy level in the combustion chamber can be setto their optimum values.

The inventive system is advantageously further developed by the exhaustgas cooler being arranged in a separate heat exchanger circuit. The heatexchanger cooler can thus operate autonomously without being influencedby other components of the motor vehicle. Likewise other components ofthe cooling system of the vehicle are not influenced by the exhaust gascooler. The autonomous cooling circuit then comprises a separate coolerand a separate coolant pump.

It can however also be useful for the exhaust gas cooler to be arrangedin the engine coolant circuit. In this way components of the enginecoolant circuit can be used for exhaust gas cooling, so that overall anefficient system is implemented.

Similarly there can be provision for the exhaust gas cooler to bedisposed as an engine oil or transmission oil heat exchangerrespectively. Existing components of the vehicle can also be used bythis.

The invention is developed in a particularly advantageous way by theprocess values or the values determined using a technical model beingassigned to at least one of the following variables:

-   -   Exhaust gas temperature,    -   Recirculated exhaust gas mass or quantity respectively,    -   Air/fuel temperature,    -   Air/fuel mass or quantity respectively,    -   Induction gas temperature,    -   Induction gas mass or quantity respectively,    -   Coolant temperature or oil temperature of the coolant or oil        flowing through the exhaust gas cooler and    -   Coolant mass or oil mass or coolant quantity or oil quality of        the coolant flowing through the exhaust gas cooler.

If the term “quantity” is used below, this can also mean a “mass” andvice versa. The current exhaust gas temperature and the recirculatedexhaust gas quantity are known in modern engine controls as engineoperation variables. They can either be calculated on the basis oftechnical models or measured directly via corresponding sensors. Thesame applies to the air/fuel quality and the air/fuel temperature. Thecoolant temperatures and the oil temperatures are also known. If thequantity of coolant or quantity of oil respectively flowing through theexhaust gas heat exchanger are further known, with a knowledge of theheat exchanger characteristics the exhaust gas temperature at the heatexchanger outlet and thereby the mixture temperature of the inductionair can be determined.

It has proved especially useful for a temperature sensor to record theair/fuel temperature, a temperature sensor to record the exhaust gastemperature at the engine exhaust, an air mass or quantity measurementdevice respectively to record the air/fuel mass or quantity and anexhaust gas mass or quantity measuring device to record the exhaust gasmass or quantity to be provided. From these variables, with a knowledgeof specific models or specific characteristics respectively thesignificant variables for reliable regulation of the induction gastemperature can be determined.

Thus the system is usefully further developed by the induction gastemperature being calculated in accordance with the equationT _(ASG) ={dot over (m)} _(FG) C _(p,FG) +{dot over (m)} _(AG) C _(p,AG)with{dot over (m)}_(FG): Air/fuel mass flow{dot over (m)}_(AG) Exhaust gas mass flowT_(FG): Air/fuel temperatureT_(AG): Exhaust gas temperatureT_(ASG) Induction gas temperaturec_(p,FG): Heat capacity of the air/fuel mixtureC_(p,AG): Heat capacity of the exhaust gas.

The induction gas temperature can thus be determined with a knowledge ofmeasured, known variables or also variables calculated from technicalmodels.

In this connection it is useful for the exhaust gas temperature at theheat exchanger output to be calculated using the following equationsystem:|Δ{dot over (Q)} _(KM) |=|Δ{dot over (Q)} _(AG) |={dot over (Q)} _(WT)Δ{dot over (Q)} _(KM) ={dot over (m)} _(KM) C _(p,KM)(T _(KM,OUT) −T_(KM,IN))Δ{dot over (Q)} _(AG) ={dot over (m)} _(AG) C _(p,AG)(T _(AG,IN) −T_(AG,OUT)){dot over (Q)} _(WT) =kAΔT _(m)with{dot over (Q)}: Heat flowKM: CoolantAG: Exhaust gasWT: Heat exchangerC_(p): Heat capacityk: Heat transfer coefficient of the heat exchangerA: Heating surface of the heat exchangerΔT_(m) Mean logarithmic temperature difference.

From the knowledge of the characteristics of the heat exchanger, meaningespecially in the knowledge of the parameters k and A, taking intoaccount the mean logarithmic temperature difference ΔT_(m), the heatflow {dot over (Q)}_(WT) present in the heat exchanger can becalculated. From this, in the knowledge of mass flows, heat capacitiesand further temperatures, the exhaust gas temperature at the heatexchanger output T_(AG,OUT) is produced.

The invention builds on the generic method in that the temperatureincrease of the fresh air from T₁ to T₂ is explicitly used to influencethe temperature level and thereby the energy level in the combustionchamber. In this way the advantages and special features of theinventive system are also implemented within the framework of a method.This also applies to the especially preferred embodiments of theinventive method specified hereafter.

The method is further developed in an especially advantageous manner byexhaust gas from an earlier combustion cycle being fed into fresh air orinto a mixture featuring fresh air respectively, in order to provide,after fuel has been injected, an air/fuel/exhaust gas mixture with anenergy level advantageous for combustion.

The method stands out as being particularly advantageous if thecompression is performed by an exhaust gas turbocharger.

Equally the method is useful if the compression is performed by acompressor.

Usefully there is furthermore provision for the expansion to beperformed on a throttle valve.

The method is further developed in an especially advantageous manner bythe temperature T₂ being recorded after the expansion, so that this canthen be taken into account within the framework of regulating theinduction gas temperature.

In an especially preferred embodiment of the inventive method there isprovision for exhaust gas to be cooled in a heat exchanger operating asan exhaust gas cooler to lower the temperature of the recirculatedexhaust gas for the induction gas temperature to bet set or regulatedthrough influencing of the coolant throughflow through the exhaust gascooler by means of a coolant setting valve, taking into account measuredvalues or values determined from technical models.

It is especially advantageous for the process values or the valuesdetermined from technical models to be assigned to at least one of thefollowing variables:

-   -   Exhaust gas temperature,    -   Recirculated exhaust gas mass or quantity respectively,    -   Air/fuel temperature,    -   Air/fuel mass or quantity respectively,    -   Induction gas temperature,    -   Induction gas mass or quantity respectively,    -   Coolant temperature or oil temperature of the coolant or oil        flowing through the exhaust gas cooler and    -   Coolant mass or oil mass or coolant quantity or oil quantity of        the coolant or oil respectively flowing through the exhaust gas        cooler.

It has proved to be especially useful for the air/fuel temperature, theexhaust gas temperature at the engine outlet, the air/fuel mass orquantity respectively and the exhaust gas mass or quantity respectivelyto be measured.

The method is further developed in a useful manner by the induction gastemperature being calculated according to the equationT _(ASG) ={dot over (m)} _(FG) C _(p,FG) +{dot over (m)} _(AG) C _(p,AG)with{dot over (m)}_(FG): Air/fuel mass flow{dot over (m)}_(AG) Exhaust gas mass flowT_(FG): Air/fuel temperatureT_(AG): Exhaust gas temperatureT_(ASG) Induction gas temperaturec_(p,FG): Heat capacity of the air/fuel mixtureC_(p,AG): Heat capacity of the exhaust gas.

In this connection it is useful for the exhaust gas temperature at theheat exchanger output to be calculated using the following equationsystem:|Δ{dot over (Q)} _(KM) |=|Δ{dot over (Q)} _(AG) |={dot over (Q)} _(WT)Δ{dot over (Q)} _(KM) ={dot over (m)} _(KM) C _(p,KM)(T _(KM,OUT) −T_(KM,IN))Δ{dot over (Q)} _(AG) ={dot over (m)} _(AG) C _(p,AG)(T _(AG,IN) −T_(AG,OUT)){dot over (Q)} _(WT) =kAΔT _(m)with{dot over (Q)}: Heat flowKM: CoolantAG: Exhaust gasWT: Heat exchangerC_(p): Heat capacityk: Heat transfer coefficient of the heat exchangerA: Heating surface of the heat exchangerΔT_(m) Mean logarithmic temperature difference.

The invention is based on the knowledge that, by explicitly influencingor explicitly taking into account the air/fuel temperature, very fineand precise control can be exerted on the energy level in the combustionchamber of the internal combustion engine. As well as the principle ofexhaust gas recirculation, this makes a further available a furtherindependent instrument for influencing the temperature level and therebyfor combustion process control. The invention in particular offers theadvantage that, starting from cold-start conditions, under which HCCIoperation is not possible because the temperature level is too low, theair/fuel mixture is heated up and thus an earlier switchover into thelower-emission HCCI mode is possible. In an especially preferredembodiment it is especially useful that the controlled setting of theexhaust gas temperature by means of exhaust gas cooling, in addition tothe exhaust gas recirculation rate and the principle of compression andexpansion, makes available a further independent adjustment variable toinfluence the temperature level and thereby the energy level in thecombustion chamber and thereby an additional means of controlling thecombustion process. The influence of the process is exerted in respectof the ignition point of the compressed air/fuel/exhaust gas mixture andthe resulting variables produced from it, such as pressure curve andcombustion, peak pressure, 50% mass fraction burnt point and speed ofcombustion. These variables in their turn are decisively responsible forthe overall engine behavior in respect of its efficiency, emissions,ride disturbance and acoustics. The invention ties in with the fact thatin modern engine management systems all the relevant information andoperating variables, for example temperatures and masses of materials orquantities, which are needed for control of the HCCI combustion processby means of exhaust gas temperature regulation are already available.The invention can also be effectively used to allow for changedenvironmental or operating conditions in combustion engines, as forexample is the case for engine hot running or in summer/winter mode atgreatly differing ambient temperatures.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now explained with reference to the accompanyingdrawings on the basis of preferred embodiments.

The figures show:

FIG. 1 a temperature-entropy diagram to explain the basic thermodynamicprinciples in a preferred embodiment of the present invention;

FIG. 2 a schematic diagram of a preferred embodiment of an inventivesystem;

FIG. 3 a schematic diagram of an inventive system; and

FIG. 4 a functional block diagram to explain the induction gastemperature regulation within the context of a method in accordance withthe invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a temperature-entropy diagram to explain the basicthermodynamic principles of a preferred embodiment of the presentinvention. The diagram shows the temperature-entropy graphs in a gas fortwo different pressures p1 and p₂. If a gas is compressed, starting froma pressure p₁ and temperature T₁, to the pressure p₂, this process doesnot run along an isentrope (process 1-2 s), but under entropy increase(process 1-2). If an expansion occurs after the compression, meaningthat the pressure falls, this does not occur along an isentrope (process2-3 s), but likewise under an increase of entropy (process 2-3). Theprocesses for increasing pressure from p1 to p₂ shown here and thesubsequent expansion to the output level p₁ represent a special case. Anexpansion to any other pressure level also occurs under an increase inentropy. Finally the gas, after compression from of p₁ to p₂ andexpansion from p₂ to p₁, has a higher temperature level than before thecompression; The temperature has increased from T1 to T3. The desiredtemperature change can thus be set for an internal combustion engine viathe degree of compression and the subsequent expansion, for example onthe throttle valve.

FIG. 2 shows a schematic diagram of a preferred embodiment of aninventive system. It shows an internal combustion engine 10 with anexhaust gas recirculation device 14 and exhaust gas turbocharger 16. Athrottle valve 18 is arranged in the inlet of the internal combustionengine 10. The exhaust train of the internal combustion engine 10 isequipped with an exhaust gas cooler 32. The particular features of theexhaust gas cooler 32 are not entered into within the context of thepresent diagram shown in FIG. 2. An exhaust gas recirculation valve 36is provided in the exhaust gas recirculation system 14. The systemfurther comprises at different points measuring devices or sensors 20,22, 24, 26, 28, 30 respectively, of which the output signals can be fedto a control/computation unit 34. In detail the following are provided:An air mass measurement device 28, a temperature sensor 20, which isarranged in the direction of flow of the fresh air current upstream fromthe throttle valve 18 to record the fresh air temperature, a temperaturesensor 22 to record the temperature of the induction gas before it flowsinto the combustion chamber 12 of the internal combustion engine 10, anexhaust gas temperature sensor 24 as well as a temperature sensor 26 forrecording the temperature at the air/exhaust gas mixture point. Thesesensors do not absolutely have to be present to implement the presentinvention. For example the temperature sensor 26 can be left out if theinduction gas temperature is determined in accordance with thecalculations explained in conjunction with FIG. 3. Output signals ofthese measuring devices and sensors 20, 22, 24, 26, 28 can be fed to thecontrol/regulation/computation device, which in its turn can activatecomponents of the system, such as for example the exhaust gasrecirculation valve 36, the exhaust gas cooler 32, the throttle valve 18and the exhaust gas turbocharger 16. The function of these componentscan thus be influenced and in the final analysis can contribute to thedesired energy level in the combustion chamber 12 of the internalcombustion engine 10.

The system shown in FIG. 2 operates as follows. Fresh air is sucked inand compressed by the exhaust gas turbocharger 16 which is driven by theexhaust gas flow. This compressed air must pass the throttle valve 18 sothat it comes to be expanded. On the basis of the thermodynamicprinciples shown in conjunction with FIG. 1 the air behind the throttlevalve 18 has a higher temperature than the originally induced fresh air.The air reaches the combustion chamber 12 of the internal combustionengine 10. After combustion the exhaust gas is expelled, to be cooled inan exhaust gas cooler 32. Part of the cooled exhaust gas is emitted viathe exhaust train. Part of the cooled exhaust gas 32 is recirculated viaexhaust gas recirculation system 14 and especially the exhaust gasrecirculation valve 36 to the inlet side of the internal combustionengine 10. On the basis of the signal recorded in the measuring devicesand sensors 20, 22, 24, 26, 28 the control/regulation/computation unit34 can influence the system so that in the final analysis the energylevel suitable for the HCCI operation is available in the combustionchamber 12 of the internal combustion engine 10. A significant part ofthe exhaust gas temperature regulation is described in conjunction withFIG. 4.

FIG. 3 shows a schematic diagram of an inventive system, with theespecially preferred embodiment with exhaust gas cooler beingspecifically examined here. An internal combustion engine 10 with anexternal exhaust gas recirculation device 14 is shown. The exhaust gasrecirculation device 14 comprises an exhaust gas recirculation valve 36via which the exhaust gas recirculation rate can be set. The exhaust gasrecirculation device 14 further comprises a heat exchanger 32 operatingas an exhaust gas cooler. Furthermore a coolant flows through theexhaust gas heat exchanger 32 via a coolant system 46. A cooler 48 isprovided to cool the coolant. In the present example the exhaust gasheat exchanger circuit is arranged as a parallel circuit. Howevernumerous other exhaust gas cooler variants are conceivable, in whichcase the cooler 48 can be arranged as a separate cooler; It is alsoconceivable to use the cooler for engine cooling as well. Cooling canalso be performed by the engine or transmission oil.

The coolant system 46 furthermore includes a coolant setting valve 50,via which the coolant quantity which flows through the exhaust gascooler 32 can be set.

The system shown operates as follows. Exhaust gas emerging from theinternal combustion engine 10 is partly recirculated via the exhaust gasrecirculation device 14 to the inlet side of the internal combustionengine 10. In this case the exhaust gas mass flow m_(AG) can be set bymeans of the exhaust gas recirculation valve 36. At the input of theexhaust gas cooler 32 the exhaust gas has a temperature T_(AG,IN), andat the output of the exhaust gas cooler 32 the exhaust gas has atemperature T_(AG,OUT), which is generally less than the temperature atthe input. The cooling effect of the exhaust gas cooler 32 can be set bysetting the coolant mass flow m_(KM) via the coolant setting valve 50.At the input of the exhaust gas cooler 32 the temperature has thetemperature T_(KM,IN) and at the output of the exhaust gas cooler 32 thetemperature T_(KM,OUT), with the latter generally being higher than thetemperature at the input. The coolant is then cooled in the cooler 48.The influencing of the throughflow of coolant through the exhaust gascooler 32 by the coolant setting valve 50 can thus, taking into accountmeasured values or values determined on the basis of technical models,be used to either set or regulate the induction gas temperature ofexhaust gas flowing into the internal combustion engine 10.

The exhaust gas temperature T_(AG,OUT) at the output of the exhaust gascooler 32 can in this case for example be calculated using the followingequation system:|Δ{dot over (Q)} _(KM) |=|Δ{dot over (Q)} _(AG) |={dot over (Q)} _(WT)Δ{dot over (Q)} _(KM) ={dot over (m)} _(KM) C _(p,KM)(T _(KM,OUT) −T_(KM,IN))Δ{dot over (Q)} _(AG) ={dot over (m)} _(AG) C _(p,AG)(T _(AG,IN) −T_(AG,OUT)){dot over (Q)} _(WT) =kAΔT _(m)with{dot over (Q)}: Heat flowKM: CoolantAG: Exhaust gasWT: Heat exchangerC_(p): Heat capacityk: Heat transfer coefficient of the heat exchangerA: Heating surface of the heat exchangerΔT_(m): Mean logarithmic temperature difference.

The temperature of the induction gas, referred to hereafter as TASG, canthen be determined in accordance with the following equation:T _(ASG) ={dot over (m)} _(FG) C _(p,FG) +{dot over (m)} _(AG) C _(p,AG)with{dot over (m)}_(FG): Air/fuel mass flow{dot over (m)}_(AG): Exhaust gas mass flowT_(FG): Air/fuel temperatureT_(AG): Exhaust gas temperatureT_(ASG): Induction gas temperaturec_(p,FG): Heat capacity of the air/fuel mixtureC_(p,AG): Heat capacity of the exhaust gas.

FIG. 4 shows a functional block diagram to explain the induction gastemperature regulation within the context of a method in accordance withthe invention. The functional units shown can be components of thecontrol/regulation/computation device shown in FIG. 1. The device 38 isprovided for calculating the required exhaust gas temperature. This isconnected to a device 40 for calculating the coolant throughflow of theexhaust gas cooler 32 shown in FIG. 1. The device 40 to calculate thecoolant throughflow is in its turn connected over a regulation path 42to a controller 44. Furthermore signals are shown in FIG. 2, withsignals ending with the letters AV identifying actual values, whereassignals ending with the letters SP identify setpoint values.

The induction gas temperature regulation in accordance with FIG. 4operates as follows. In accordance with engine operating conditions asetpoint value for the temperature of the induced air in the inductionmanifold (TIA_IM_SP) is specified. This is fed, together with the actualair/fuel temperature (TIA_AV) and the mass of the air/fuel fed in(MAF_KGH_AV) as well as the recycled exhaust gas (M_EGR_AV) to device 38to calculate the required exhaust temperature. Taking into account thespecific heat capacities of the fresh air (C_(p, air)) fed in and of theexhaust gas (c_(p, exhaust gas)) this device calculates the exhaust gastemperature at the mixing point (T_EGR_DOWN_SP) which is required toobtain the desired induction gas temperature in the inlet manifold. Inthe device 40 for calculating the coolant throughflow the setpoint valuedetermined by the device 38 for calculating the required exhaust gastemperature (T_EGR_DOWN_SP) is compared to the actual exhaust gastemperature at the engine outlet (T_EGR_UP_AV) before the exhaust gascooler. From the difference a coolant throughflow (M_COOL) through theexhaust gas cooler is determined which is required to obtain the desiredexhaust gas temperature at the mixing point (T_EGR_DOWN_SP). Thiscoolant flow is then implemented by a corresponding activation of anelectrical coolant pump, with other types of throughflow regulationbeing just as easily possible. The coolant throughflow is converted inaccordance with the control specified here via the regulation path 42into a specific induction gas temperature in the inlet manifold(TIA_IM_AV) with this being present after an initial settling-downphase. This induction gas temperature in the inlet manifold (TIA_IM AV)is compared with the setpoint value (TIA_IM_SP) in the controller 44. Ifthe values differ from each other, the coolant throughflow through theexhaust gas cooler is corrected by a value (AM_COOL), so that finallyvia a suitable exhaust gas temperature at the mixing point(T_EGR_DOWN_AV) the desired induction air temperature (TIA_IM_SP) is setin accordance with the setpoint.

To place the regulation explained in conjunction with FIG. 4 into abetter context with the system shown in FIG. 2 shown, details are givenbelow of where the values used for the regulation are to be measured orset respectively. The air mass measurement device 28 determines thevalue MAF_KGH_AV. The recirculated exhaust gas component M_EGR_AV isknown in the context of the exhaust gas recirculation throughcorresponding activation of the exhaust gas recirculation valve 36. Theair/fuel temperature TIA_AV is measured by the temperature sensor 20beyond the throttle valve 18. The induction gas temperature TIA_IM_AV isrecorded by the temperature sensor 22 before it enters the combustionchamber 12 of the internal combustion engine 10. The temperature sensor24 at the outlet from the combustion chamber 12 of the internalcombustion engine 10 records the exhaust gas temperature T_EGR_UP_AV. Inadditional the temperature TIA_EGR_DOWN_AV at the mixing point can berecorded by the temperature sensor 26, in which case this is however notabsolutely necessary for the regulation described in conjunction withFIG. 4.

Thus the invention can be summarized as follows: With a HCCI-enabledinternal combustion engine, which is preferably equipped with an exhaustgas recirculation device 14, a system and a method is proposed on thebasis of which the setting of the temperature level in the combustionchamber can be improved. As well as setting the temperature via theexhaust gas recirculation device 14 the temperature is influencedindependently of this as a result of the compression of the inducedfresh air by the exhaust gas turbocharger 16, with, even after theexpansion of the compressed air on a throttle valve 18, a temperatureincrease being retained, which in the final analysis can be used toinfluence the energy content of the combustion chamber 12.

The features of the invention disclosed in this description, in thedrawings and in the claims, can be of importance both individually andin any combination for implementing the invention.

1-23. (canceled)
 24. A system for influencing an induction gastemperature in a combustion chamber of an internal combustion engine,comprising: a compression device to compress induced fresh air and thefresh air having a first temperature before compression; an expansiondevice that causes an expansion of the compressed induced fresh air,with the compressed and subsequently expanded fresh air having a secondtemperature greater than the first temperature; and a temperature sensorto record the second temperature that is arranged in the direction offlow of the fuel/air with reference to the expansion device so that thiscan be taken into account within the framework of regulating theinduction gas temperature.
 25. The system in accordance with claim 24,wherein an exhaust gas recirculation device is provided to feed exhaustgas from an earlier combustion cycle to fresh air or to a mixturefeaturing fresh air, in order to provide an air/fuel/exhaust gas mixturewith an advantageous energy level for combustion after injection offuel.
 26. The system in accordance with claim 24, wherein thecompression device is an exhaust gas turbocharger.
 27. The system inaccordance with claim 24, wherein the compression device is acompressor.
 28. The system in accordance with claim 24, wherein theexpansion is performed on a throttle valve.
 29. The system in accordancewith claim 24, wherein at least one heat exchanger operating as anexhaust gas cooler is provided for reducing the temperature of there-circulated exhaust gas and a coolant setting valve is provided sothat an induction gas temperature can be set or regulated by influencingthe coolant through-flow through the exhaust gas cooler taking intoaccount measured values or values determined on the basis of technicalmodels.
 30. The system in accordance with claim 24, wherein an exhaustgas cooler is arranged in a separate heat exchanger circuit.
 31. Thesystem in accordance with claim 24, wherein the exhaust gas cooler isarranged in an engine coolant circuit.
 32. The system in accordance withclaim 24, wherein an exhaust gas cooler is designed as an engine ortransmission oil heat exchanger respectively.
 33. The system inaccordance with claim 24, wherein the measured values or the valuesdetermined in accordance with technical models are assigned to at leastone of the variables selected from the group consisting of: exhaust gastemperature, recirculated exhaust gas mass, recirculated exhaust gasquantity, air/fuel temperature, air/fuel mass, air/fuel quantity,induction gas temperature, induction gas mass, induction gas quantity,coolant temperature, oil temperature of the coolant, oil flowing throughthe exhaust gas cooler, coolant mass, oil mass, coolant quantity, oilquantity of the coolant, and oil flowing through the exhaust gas cooler.34. The system in accordance with claim 24, wherein a temperature sensorto record the air/fuel temperature, a temperature sensor to record theexhaust gas temperature at the engine exhaust, an air mass or quantitymeasurement device respectively to record the air/fuel mass or quantity,and an exhaust gas mass or quantity measuring device to record theexhaust gas mass or quantity are provided.
 35. The system in accordancewith claim 24, wherein the induction gas temperature is calculated inaccordance with equation$T_{ASG} = \frac{{{\overset{.}{m}}_{FG}T_{FG}C_{p,{FG}}} + {{\overset{.}{m}}_{AG}T_{AG}C_{p,{AG}}}}{{{\overset{.}{m}}_{FG}C_{p,{FG}}} + {{\overset{.}{m}}_{AG}C_{p,{AG}}}}$with {dot over (m)}_(FG): Air/fuel mass flow {dot over (m)}_(AG):Exhaust gas mass flow T_(FG): Air/fuel temperature T_(AG): Exhaust gastemperature T_(ASG): Induction gas temperature c_(p,FG): Heat capacityof the air/fuel mixture C_(p,AG): Heat capacity of the exhaust gas. 36.The system in accordance with claim 24, wherein the exhaust gastemperature at the heat exchanger outlet is calculated using thefollowing equation system:|Δ{dot over (Q)} _(KM) |=|Δ{dot over (Q)} _(AG) |={dot over (Q)} _(WT.);Δ{dot over (Q)} _(KM) ={dot over (m)} _(KM) C _(p,KM)(T _(KM,OUT) −T_(KM,IN))Δ{dot over (Q)} _(AG) ={dot over (m)} _(AG) C _(p,AG)(T _(AG,IN) −T_(AG,OUT)){dot over (Q)} _(WT) =kAΔT _(m) with {dot over (Q)}: Heat flow KM:Coolant AG: Exhaust gas WT: Heat exchanger C_(p): Heat capacity k: Heattransfer coefficient of the heat exchanger A: Heating surface of theheat exchanger ΔT_(m) Mean logarithmic temperature difference.
 37. Amethod for influencing an induction gas temperature of an internalcombustion engine, comprising: compressing induced fresh air having afirst temperature before compression; expanding the compressed inducedfresh air such that the compressed and subsequently expanded fresh airhas a second temperature greater than the first temperature; recordingthe second temperature after the expansion so it can be taken intoaccount within a framework of a regulation of the induction gastemperature.
 38. The method according to claim 37, wherein exhaust gasfrom an earlier combustion cycle is fed into fresh air or into a mixturefeaturing fresh air respectively in order to provide an air/fuel/exhaustgas mixture with an energy level advantageous for combustion.
 39. Themethod in accordance with claim 37, wherein the compression is performedby an exhaust gas turbocharger.
 40. The method in accordance with claim37, wherein the compression is performed by a compressor.
 41. The methodin accordance with claim 37, wherein the expansion is performed on athrottle valve.
 42. The method in accordance with claim 37, whereinexhaust gas is cooled in a heat exchanger operating as an exhaust gascooler for reducing a temperature of a recirculated exhaust gas and byinfluencing the coolant throughflow through the exhaust gas cooler bymeans of a coolant setting valve taking into account measured values orvalues determined from technical models, the induction gas temperatureis set or regulated respectively.
 43. The system in accordance withclaim 37, wherein the measured values or the values determined inaccordance with technical models are assigned to at least one of thevariables selected from the group consisting of: exhaust gastemperature, recirculated exhaust gas mass, recirculated exhaust gasquantity, air/fuel temperature, air/fuel mass, air/fuel quantity,induction gas temperature, induction gas mass, induction gas quantity,coolant temperature, oil temperature of the coolant, oil flowing throughthe exhaust gas cooler, coolant mass, oil mass, coolant quantity, oilquantity of the coolant, and oil flowing through the exhaust gas cooler.44. The method in accordance with claim 42, wherein the air/fueltemperature, the exhaust gas temperature at the engine exhaust, theair/fuel mass or quantity respectively and the exhaust gas mass orquantity respectively are measured.
 45. Method in accordance with claim44, wherein the induction gas temperature is calculated in accordancewith equation$T_{ASG} = \frac{{{\overset{.}{m}}_{FG}T_{FG}C_{p,{FG}}} + {{\overset{.}{m}}_{AG}T_{AG}C_{p,{AG}}}}{{{\overset{.}{m}}_{FG}C_{p,{FG}}} + {{\overset{.}{m}}_{AG}C_{p,{AG}}}}$, with {dot over (m)}_(FG): Air/fuel mass flow {dot over (m)}_(AG):Exhaust gas mass flow T_(FG): Air/fuel temperature T_(AG): Exhaust gastemperature T_(ASG): Induction gas temperature c_(p,FG): Heat capacityof the air/fuel mixture C_(p,AG): Heat capacity of the exhaust gas. 46.The method in accordance with claim 42, wherein the exhaust gastemperature at the heat exchanger outlet is calculated using thefollowing equation system:|Δ{dot over (Q)} _(KM) |=|Δ{dot over (Q)} _(AG) |={dot over (Q)} _(WT);Δ{dot over (Q)} _(KM) ={dot over (m)} _(KM) C _(p,KM)(T _(KM,OUT) −T_(KM,IN));Δ{dot over (Q)} _(AG) ={dot over (m)} _(AG) C _(p,AG)(T _(AG,IN) −T_(AG,OUT));{dot over (Q)} _(WT) =kAΔT _(m) with {dot over (Q)}: Heat flow KM:Coolant AG: Exhaust gas WT: Heat exchanger C_(p): Heat capacity k: Heattransfer coefficient of the heat exchanger A: Heating surface of theheat exchanger ΔT_(m) Mean logarithmic temperature difference.